Copolymers of ethylene and a monoolefinically unsaturated polar comonomer such as vinyl acetate, methyl methacrylate, acrylic acid, and the like have been widely employed for their adhesive properties particularly for the reason that they form firm bonds to nonporous substrates such as metals or glass.
Even though the aforementioned copolymers exhibit superior qualities as adhesives their application is limited by two significant shortcomings. In damp or humid environments or in applications where the adhesive can otherwise be contacted by water, the adhesive bond fails. Furthermore, in those environments where arctic or subarctic conditions are encountered, for example, below about -40.degree. F., the adhesives become inflexible and fracture under dynamic conditions.
The above significant shortcomings are said to be overcome by compositions comprising a blend of an adhesive copolymer of ethylene and a monoolefinically unsaturated polar comonomer, for example, vinyl acetate, in combination with an olefin rubber, preferably a rubbery copolymer of ethylene and propylene, exhibit excellent adhesive properties, particularly when applied to non-porous surfaces such as metals as taught in U.S. Pat. No. 4,332,655. Unfortunately these blends of olefin rubber and the ethylene copolymers (all of which possess melt indexes of less than 500 dg/min.) result in adhesive formulations having very high melt viscosities and thus are very difficult to apply, particularly to heat sensitive materials like polyethylene.
Further, the diluents such as waxes and plasticizers, which are added to reduce the undesirably high melt viscosity and thus make the adhesive mass more flowable, have no inherent strength and generally adversely affect adhesive performance.
It is an object of this invention to provide an eastomer-ethylene copolymer blend of reduced melt viscosity which blend retains its useful adhesive properties.